Method and apparatus for bending glass sheets

ABSTRACT

METHOD AND APPARATUS FOR BENDING GLASS SHEETS IN WHICH A FLAT SHEET OF GLASS, HEATED TO BENDING TEMPERATURE, IS SUPPORTED HORIZONTALLY ABOVE A PRIMARY MOLD MEMBER HAVING A SHAPING SURFACE OF THE CURVATURE CORRESPONDING TO THE SHEET WHEN BENT. THE MOLD MEMBER IS MOVED UPWARDLY TO LIFT THE SHEET, WHEREUPON THE SHEET WILL SETTLE INTO CONTACT WITH THE SHAPING SURFACE OF THE MOLD UNDER THE INFLUENCE OF FORCES RESULTING FROM THE INERTIA OF THE SHEET AND FROM GRAVITY. A SECONDARY MOLD MEMBER, MOUNTED ABOVE THE PRIMARY MOLD MEMBER, IS PROVIDED TO ENGAGE CERTAIN SPACED PORTIONS ONLY ON THE EDGES OF THE SHEET WHICH TEND TO CURL UPWARD AS INERTIAL FORCES CAUSE THE CENTER OF THE SHEET TO INSURE THAT THESE PORTIONS WILL BE PRESSED INTO CONFORMITY WITH THE PRIMARY MOLD MEMBER.

- ab- ,1971 Gi. F.RlTT ER,JR.. ETAL 3,554,724

' METHOD AND APPARATUS FOR BENDING GLASS SHEETS Filed May 24, 196B 2% 1Nv I 'wr e 91%. :32? 9&9. Z gymmk y United States Patent 3,554,724 METHODAND APPARATUS FOR BENDING GLASS SHEETS George F. Ritter, Jr., Toledo,and Frank J. Hymore,

Oregon, Ohio, assignors to Libbey-Owens-Ford Company, Toledo, Ohio, acorporation of Ohio Filed May 24, 1968, Ser. No. 731,973 Int. Cl. C031)23/02 US. Cl. 65-107 12 Claims ABSTRACT OF THE DISCLOSURE Method andapparatus for bending glass sheets in which a flat sheet of glass,heated to bending temperature, is supported horizontally above a primarymold member having a shaping surface of the curvature corresponding tothe sheet when bent. The mold member is moved upwardly to lift thesheet, whereupon the sheet will settle into contact with the shapingsurface of the mold under the influence of forces resulting from theinertia of the sheet and from gravity. A secondary mold member, mountedabove the primary mold member, is provided to engage certain spacedportions only on the edges of the sheet which tend to curl upward asinertial forces cause the center of the sheet to sag to insure thatthese portions will be pressed into conformity with the primary moldmember.

The present invention relates to improved apparatus for bending glasssheets.

Curved sheets of glass are widely used as glazing closures for vehicles,such as automobiles or the like. To be acceptable for such application,the curved sheets must be bent to precisely defined curvaturesdetermined by the over-all styling of the vehicle and the manner ofmounting the sheet. At the same time, the sheet must meet ratherstringent optical requirements, which dictate that the viewing area ofthe window be free of optical defects which would tend to interfere withclear vision.

In general, the commercial production of curved glass sheets of theabove character includes heating the sheets to the softening point ofthe glass, bending the heated sheets to the desired curvature andthereafter cooling them in a controlled manner to a temperature belowthe annealing range of the glass.

When produced in large quantities, the sheets are heated, bent andcooled in a substantially continuous process While being movedsuccessively through a heating area, a bending area, and a cooling area.According to one procedure, the sheets are bent into conformity with theshaping surface of a single mold member by a combination of inertial andgravitational forces, which make it possible to bend the sheets rapidlywhile leaving the viewing area of the sheets completely free fromcontact with the mold member.

In this method, the sheets are supported horizontally on a concave moldmember of outline or ring-type construction which contacts the marginaledge portions only of the sheet, and bending is initiated byaccelerating the sheet bodily upwardly, whereupon the sheet will saginto contact with the shaping surface of the mold under the influence offorces resulting from the inertia of the sheet and from gravity. Afterthe mold has moved upwardly a predetermined distance it is haltedmomentarily while the sheet settles into conformity with the shapingsurface of the mold. Such a bending procedure is disclosed in thecorresponding application of George F. Ritter, Ir. Ser. No. 573,969,filed Aug. 22, 1966 now Pat. No. 3,476,540.

While this so-called inertia-gravity bending procedure has proved quitesuccessful, there is a practical limitation on the sharpness andcomplexity of the bends which can be produced thereby. This isparticularly true when a relatively sharp curve is to be formed in theend portions of the sheets where there is a tendency for the edgeportions and especially the corners to curl upward away from the shapingsurface as the inertial forces cause the central area of the sheet tosag, and the subsequent purely gravitational forces are not suflicientto cause them to settle back down again.

In order to overcome the above limitation, the present inventionprovides a supplemental mold member, engageable with a glass sheetsupported on the concave primary mold member, which will insure that thecorners, or other areas of the sheet which tend to remain out of contactwith the primary mold member, will be bent into conformity with saidprimary member while, at the same time, retaining all of the advantagesof inertiagravity type bending.

Therefore, the primary object of this invention is to provide improvedbending apparatus of the inertia-gravity type on which glass sheets canbe bent to relatively sharper and more complex curvatures thanheretofore possible.

Another object of the invention is to provide such an apparatus Whichembodies a supplemental mold member engaging selected areas of the glasssheet in order to insure that they will be bent into conformity with theshaping surface of the primary mold member.

A further object of the invention is to provide apparatus of the abovecharacter which includes means for setting the curvature produced in thesheet while the said sheet is still in contact with the primary moldmember.

Other objects and advantages of the invention will become more apparentduring the course of the following description when taken in connectionwith the accompanying drawings.

In the drawings, wherein like numerals are employed to designate likeparts throughout the same:

FIG. 1 is a side elevational view of a bending apparatus constructed inaccordance with the invention;

FIG. 2 is a perspective view of the primary and supplemental bendingmold members; and

FIG. 3 is a fragmentary sectional view depicting the mold members ofFIG. 2 in engagement with a glass sheet.

Referring now to the drawings, there is illustrated in FIG. 1 a glassbending apparatus of the type in which sheets are bent by inertial andgravitational forces. The bending apparatus 10 consists essentially of amovable lower primary bending mold member 11, a substantially stationaryupper supplemental mold member 12 and a series of supporting conveyorrolls 13, all suitably mounted Within a rigid framework 14.

In order to avoid marring of those areas of the glass sheets which willconstitute the viewing area of the fin ished window, the lower moldmember 11 is of outline or ring-type construction having a shapingsurface 15 which engages only the marginal edge portions of the sheet.The shaping surface 15 is generally concave and is formed on a shapingelement 16, which is supported from a base member 17 by a plurality ofsupporting bars 18.

The lower mold member 11 is vertically movable to lift a glass sheet 19to be bent from the conveyor rolls 13 and to initiate the inertial forcerequired to promote bending. Therefore, in order to provide clearancefor the rolls 13, the shaping element 16 is made up of a plurality ofsections including transversely disposed end sections 20, and spacedlongitudinal bar portions or segments 21 between which the conveyorrolls 13 are located.

The base member 17 of the lower mold member 11 is fastened to a carriage22, such as by bolts (not shown) received in slots 23 in said basemember, and the carriage is supported by telescoping guide members 24which allow vertical movement only, said vertical movement beingprovided by the ram 25, of a pressure cylinder 26, which bears againstthe bottom of the carriage.

The glass sheets 19, which have been heated to the desired softeningtemperature, are transferred from a furnace (not shown) into the bendingapparatus on entry conveyor rolls 27 and are received in position to bebent on the rolls 13. As each sheet approaches the bending apparatus itactuates a photocell or other detection device, thereby energizingsuitable timing mechanisms which initiate and thereafter control theactions of the various components of the bending apparatus.

As each glass sheet 19 arrives in position above the mold member 11 itis halted by engagement of its leading edge with locator stops 28 (oneof two shown) which are moved into and out of the path of sheet movementby pressure cylinders 29 mounted on the base member 17. Upon anappropriate signal from the associated timing device fluid pressure isapplied to the lower end of the cylinder 26 causing the ram to rapidlymove the mold member 11 upward lifting the sheet from the supportingconveyor rolls 13. As the sheet 19 is moved bodily upward by the mold,inertia forces acting on the glass cause it to sag. Once the saggingaction has started, natural gravitational forces acting thereon aregenerally sufiicient to cause the heat softened sheet to continuebending and assume the concave contour of the shaping surface 15, by thetime, or shortly after the mold member 11 has reached the limit of itsupward movement.

In most cases the above-described procedure is adequate to completelyform a sheet to the desired curvature, such that the bent sheet can belowered back onto the conveyor rolls for transfer out of the bendingapparatus. In some situations, however, the curvature in certain areasof the sheet, particularly at the corners thereof, may be such thatinertia and gravity forces alone are not sufficient to cause the sheetto bend into conformity with the mold shaping surface. In fact, there isa tendency, regardless of the curvature of the sheet, for the corners tocurl upward away from the shaping surface as the sudden upward movementof the mold causes the unsupported central area of the sheet to sag.Although the corners will generally sag back down into conformity withthe shaping surface this may not always occur, especially when theradius of curvature is relatively small or if compound curves are to beformed.

Therefore, in accordance with the invention, there is provided asupplemental upper mold member 12 which is aligned with the lower moldmember 11 and has a shaping element comprising four L-shaped segments30, as shown in FIG. 2, which engage only the corners of the sheet. Eachof the four segments 30 is suspended from a horizontal base member 31 bydepending support rods 32, each of said segments having a generallyconvex shaping surface 33 formed on its bottom face which iscomplementary to the opposed portion of the shaping surface 15 of thelower shaping element 16 as illustrated in FIG. 3.

The upper supplemental mold member 12, which remains substantiallystationary, is attached to a rigid frame member 34 by means of boltsreceived in slots 35 or in some other suitable manner. The rigid framemember 34 is resiliently suspended from a mounting frame 36 dependingfrom the main framework 14 by bolts 37. Springs 38 surrounding each bolt37, are interposed between the mounting frame 36 and the frame member 34and limit the amount of force that is applied by the segments 30 whenthey contact the glass at the upper limit of movement of the lower moldmember 11.

In order to insure that the glass sheet 19 will retain the desiredcurvature while it is being transferred from the bending apparatus 10 toanother area for additional treatment, such as annealing or tempering,cooling tubes 39 are mounted on the lower mold member 11, between theshaping element 16 and the base 17. These tubes, which extendtransversely across the full width of the shaping element 16 areprovided with upwardly directed orifices so that cooling air may bedirected against the bottom surface of the bent sheet as it is beinglowered back onto the conveyor rolls 13. The effect of this cooling isto reduce the temperature of the sheet a sufiicient amount to cause itto permanently set in the curved configuration without significantlyaffecting any further heat treatment which may be performed upon itsexit from the bending apparatus.

In a typical operational cycle of the illustrated embodiment, a heatsoftened glass sheet 19 enters the bending apparatus 10 upon entryconveyor rolls 27 and is deposited on the rolls 13 within the apparatus,whereupon it is stopped by the locator stops 28 when it becomes alignedwith the shaping element 16 of the lower mold member 11. The mold member11 then moves quickly upward, by virture of the force applied :by theram 25, lifting the sheet off the rolls 13. The combined effffects ofinertial and gravitational forces then cause the glass sheet to sag intoconformity with the shaping surface 15 of the lower mold member 11. Asthe mold member approaches the end of its upward travel the four cornerportions of the sheet are engaged by the downwardly directed segments 30of the supplemental mold member 12.

While, as pointed out above, the combined forces of inertia and gravitywill ordinarily be sufficient to cause the sheet to conform to theshaping surface 15 upon upward movement of the lower mold member, thebending segments 30 of the supplemental mold member will insure that thecorner portions of the sheet will always be pressed down into conformitywith the corner areas of the lower mold member.

When the mold member 11 reaches the upper limit of its travel, it isstopped momentarily to insure that the sheet has sagged into its bentconfiguration. Fluid pressure is then applied to the upper end ofcylinder 26 causing the mold member 11 to move downward depositing thebent sheet 19 upon the rolls 13.

During upward movement of the glass sheet 19 the locator stops 28 aremoved downward to an out-of-theway position below the supportingsurfaces of the rolls 13, so that when the bent sheet 19 is deposited onthe rolls it is free to be transferred thereby out of the bendingapparatus 10 upon exit conveyor rolls 40. As the bent sheet nears therolls 13, cooling air is applied by the tubes 39 to the bottom surfaceof the sheet 19 to set it to the desired curvature before it is receivedon the rolls 13.

Although the illustrated mold is of rectangular configuration, it iscontemplated that similar supplemental mold members can be utilized inconjunction with a variety of shapes formed by the inertia-gravitymethod. It Will also be appreciated that the shape and location of thesegments 30 will depend upon the exact configuration of the bent sheetdesired, and that such segments may be used in locations about themarginal edges other than at corners, when, because of the nature of thebend, there may be a tendency for that portion of the sheet to lift andremain off the shaping surface after the application of the inertial andgravitational forces.

It is to be understood that the form of the invention herewith shown anddescribed is to be taken as an illustrative embodiment only of the sameand that various changes in the shape, size and arrangement of parts maybe resorted to without departing from the spirit of the invention.

We claim:

1. Apparatus for the horizontal bending of glass sheets, the combinationof a lower primary mold member having a shaping element with a marginaledge shaping surface of a desired outline and curvature formed thereon,

means for supporting a heat softened glass sheet in position above saidshaping surface, means for moving said mold member upwardly between alower and upper limit of travel to lift said sheet bodily from saidsupporting means thereby creating combined inertial and gravitationalforces to initiate the bending of said sheet into conformity with saidshaping surface, and a substantially stationary secondary mold memberspaced above said primary mold member, said secondary mold membercomprising a shaping element having formed thereon a shaping surfacealigned with and complemental to a portion only of the marginal edgeshaping surface of said primary mold member, said complemental shapingsurfaces being engageable with opposite surfaces of a glass sheetsupported on said primary mold member when said primary mold memberreaches the upper limit of travel.

2. Apparatus for bending glass sheets as defined in claim 1, in whichthe shaping element of said secondary mold member comprises at least onebar section aligned with and complemental to a portion only of themarginal edge shaping surface of the primary mold member.

3. Apparatus for bending glass sheets as defined in claim 1, in whichthe primary mold member is of ringtype configuration and the secondarymold member is provided with a plurality of spaced shaping surfacesdisposed opposite complemental portions of the shaping surface of theprimary mold member.

4. Apparatus for bending glass sheets as defined in claim 2, in whichsaid bar section is substantially L- shaped in plan and is aligned witha corner of the shaping surface of said primary mold member.

5. Apparatus for bending glass sheets as defined in claim 1, includingmeans for directing a cooling medium against the bottom surface of thesheet after bending and while the sheet is still supported on saidprimary shaping surface.

6. Apparatus for bending glass sheets as defined in claim 3, includingcooling tubes disposed below the shaping surface of said primary moldmember, said tubes having orifices formed therein operable to directstreams of cooling gas against the bottom surface of said sheet after itis bent in conformity with said shaping surface and while the sheet isstill supported by said primary shaping surface.

7. In apparatus for bending each of a plurality of heat softened glasssheets moving successively along a predetermined substantiallyhorizontal path, a lower primary mold member having an upwardly facingmarginal edge shaping surface, an upper secondary mold member, and aconveyor having a horizontal run extending along said path between saidupper and lower mold members for receiving a sheet to be bent and forpositioning it between said mold members, said primary mold member beingvertically movable between a lower and upper limit of travel to bodilylift said sheet from said conveyor causing the application of inertialand gravitational forces to said sheet to initiate bending of the sameinto conformity with the shaping surface on said primary mold member,and said upper secondary mold member comprising a bar vertically spacedfrom a section of the marginal edge shaping surface of the primary moldmember and having a shaping surface aligned therewith and complementalthereto, said shaping surface on said secondary mold member beingengageable with the upper surface of said glass sheet when the lowersurface thereof is in contact with said upwardly facing shaping surfaceat the upper limit of travel of said primary mold member.

8. Apparatus for bending glass sheets as defined in claim 7, in whichsaid bar is substantially L-shaped in plan corresponding to a cornerportion of said upwardly facing shaping surface.

9. Apparatus for bending glass sheets, comprising a horizontal lowerprimary mold member having a shaping element with an upwardly facingshaping surface of outline configuration formed thereon, means forsupporting a heat softened glass sheet in bending position above saidshaping surface, means for moving said mold member bodily upward betweena lower and upper limit of travel to lift said sheet and initiatebending of the same under the influence of inertial and gravitationalforces, and a substantially stationary upper, secondary mold memberspaced above said primary mold member and having a shaping element witha shaping surface formed thereon, said secondary shaping surface beingaligned with and complementary to a portion only of said upwardly facingshaping surface and engageable with a marginal portion of the uppersurface of said sheet when said primary mold member is at the upperlimit of its travel.

10. Apparatus for bending glass sheets as defined in claim 9, in whichthe primary mold member is of ring type configuration and in which thesecondary mold member comprises a plurality of spaced shaping elementshaving shaping surfaces disposed opposite complemental portions of theshaping surface of said primary mold member.

11. Apparatus for bending glass sheets comprising a lower primarymolding member having a shaping surface of a desired outline andconfiguration formed thereon, means for supporting a heat softened glasssheet in a plane above and in bending relation to said shaping surface,means for moving said molding member upwardly to lift said sheet bodilyfrom said supporting means and create combined inertial andgravitational forces to initiate the bending of said sheet intoconformity with said shaping surface, and a supplemental molding memberlocated above said plane and having formed thereon a shaping surfacealigned with and complemental to a portion only of the shaping surfaceof said primary molding member, said complemental shaping surfaces beingengageable with opposite surfaces of a glass sheet supported on saidprimary molding member after said initial bending to insure said sheetbeing finally bent into conformity with the shaping surface of saidprimary molding member.

12. In a method of bending glass sheets, the steps of heating a sheet tothe softening point of the glass, supporting the heated sheet in asubstantially horizontal plane and in bending relation to a primarycontoured outline shaping surface disposed below said plane and shapedto the curvature desired in the sheet when bent and to a supplementalshaping surface disposed above said plane and in alignment with andcomplemental to a portion only of said primary shaping surface, movingsaid primary shaping surface upwardly through said plane to lift saidsheet bodily from said plane and create an inertial force which whencombined with the force of gravity initiates the bending of said sheetinto conformity with said primary shaping surface, and thereafterengaging a marginal portion of the upper surface of said sheet with saidsupplemental shaping surface to urge said sheet into contact with saidprimary shaping surface and insure said sheet being finally bent intoconformity therewith.

References Cited UNITED STATES PATENTS 3,459,526 8/1969 Stickel et a1.65--268 3,476,540 12/1969 Ritter et al 65--107 S. LEON BASHORE, PrimaryExaminer S. R. FRIEDMAN, Assistant Examiner US. Cl. X.R. 65-287

